Sunday, April 26, 2009

Finally, Some Clues on the Domestication of Rice

The subtitle to this blog promises posts about "the origins of agriculture", although the field is so slow moving that I have not posted on the topic in three years and have not reported meaningful research here since speculating on religion as a driver.

Fortunately, others are doing active research on agricultural origins even if I am not. Dr. Dorian Fuller of the Institute of Archaeology at University College London has cracked a very special nut, indeed. He and his team have located substantial evidence of the location and timing of rice domestication in the Lower Yangtze region of Zhejiang, China.

Dr. Fuller and his colleagues discovered a location where the local diet shifted dramatically from a hunter-gatherer lifestyle to an agricultural one over a mere three hundred years. That alone is fascinating and an important discovery. Equally interesting was the dating of the shift, from 6900 to 6600 years ago. That places rice domestication in a timeframe fully two thousand years later than thought and lends serious support to diffusion theories (versus parallel development).

The process used by Fuller collected mixtures of midden material from the site, and painstakingly separated wild rice remains from domesticated rice remains. Specifically, they looked at spikelets, the place where rice seeds attach to stalks. Like other domesticated plants, rice underwent a genetic shift to retain the seeds for harvest by humans by a process of artificial selection. The shape of the spikelets is sufficiently different as to be distinguishable.

There is a nice scanning electron microscope image of a wild rice spikelet base at the Agricultural Biodiversity Weblog.

The last I heard, Londo's investigation1 was still suggesting multiple independent origins of rice in Southeast Asia and lower China. Hopefully Fuller's paper2 will put that to rest. Londo at least admitted that his team wasn't certain.

Wikipedia's entry on rice says, "Rice has been cultivated in Asia likely over 10,000 years." It is clearly time to correct that entry and, more broadly, correct the education of literally billions of people who are taught it. I really need to get back to work on my Origins of Agriculture summary and update it with these findings.

References:
[1] Londo, J.P., Chiang, Y-C, Hung, K-H, Chiang, T-U and Schaal, B.A. (2006). "Phylogeography of Asian wild rice, Oryza rufipogon, reveals multiple independent domestications of cultivated rice, Oryza sativa". PNAS, http://www.pnas.org/content/103/25/9578.long

[2] Fuller, D.Q., Qin, L., Zheng, Y., Zhao, Z., Chen, X., Hosoya, L.A. and Sun, G-P (2009, March 20). The Domestication Process and Domestication Rate in Rice: Spikelet Bases from the Lower Yangtze, Science 20 March 2009, 323/5921, pp. 1607-1610, http://www.sciencemag.org/cgi/content/abstract/323/5921/1607

6 comments:

  1. The really interesting question, I believe, is the relationship between japonica and indica varieties. They share an identical non-shattering mutation, but not a whole lot else. Could it be that the non-shattering gene from japonica introgressed with the wild population, which then re-introgressed, as it were, with the indicas that were being independently domesticated?

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  2. You may also be interested to hear the interview that Quirks and Quarks did with Dr Fuller (if you haven't already):
    http://www.cbc.ca/quirks/archives/08-09/qq-2009-04-11.html#2

    Also, since you mentioned the role of religion in your top paragraph, that episode of Quirks and Quarks also included a story on the science of religion:
    http://www.cbc.ca/quirks/archives/08-09/qq-2009-04-11.html#4

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  3. Dorian does not imply that there are can't be multiple origins and the hypothesis is still very much alive. Spikelet bases are nice because they allow archaeologists to systematically compare the process from wild to domesticated across sites. Such comparative work would be very important to get further evidence for origins and dispersals.

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